A pair, , is a known plaintext-ciphertext pair with respect to a principal, I , and key, k if and only if
We will use the term known pair to refer to a known plaintext-ciphertext pair. A principal may know that two pairs are encrypted under the same key even though the key is not known to the principal. For a particular block encryption function, it may be the case that for any p and c . However, in our analysis, it is of interest to know this fact in the context of receiving particular c and associating it with sets of under the same k . Knowledge of a pair does not imply knowledge of the corresponding key. That is knowing or does not imply knowing k .